In a conventional garden or utility sprayer, it is common to have a cylindrical tank in the top of which a hand pump is positioned for compressing air in the tank above the liquid to be dispensed. The conventional hand pump consists of a cylinder having a threaded cap for attachment to a threaded inlet port located on the top of the tank. A handle is disposed outside of the cap, and a connecting rod passes down through the cap to attach to a plunger cup located in the cylinder. The handle and plunger cups are threaded on opposed ends of the piston rod. The bottom of the cylinder is closed off with a spring-actuated valve which allows air to be driven out of the cylinder into the tank while blocking the liquid in the tank from filling the cylinder on the return stroke of the plunger cup. The plunger cup is equipped with a similar valve which allows air to enter the cylinder on the return stroke of the piston rod but which closes the plunger cup on the compression stroke.
It is obvious from the above description that a conventional manual pump for a sprayer incorporates many parts subject to failure or accidental disassembly during use. For example, it is not uncommon for the connecting rod to become disconnected from either the plunger cup or the handle when in use. Also, it is not uncommon for the spring-actuated valve closing the bottom of the cylinder or the valve closing the plunger cup to become worn preventing a full closure thereby disabling the pump. There is nothing more frustrating than carefully mixing a solution of fertilizer solution and loading it into the tank and then installing the pump only to find out that the plunger cup has fallen off the connecting rod because the nut, not visible in the pump cylinder, has fallen off. The pump has to be removed and carefully rinsed before even any attempt can be made to repair the defective pump.